Alvin, Simon, and Theodore, along with the Chipettes-- Brittany, Jeanette, and Eleanor--set up a surprise birthday bash for Dave that also serves as a good-luck party for the Chipettes, who are scheduled to be guest-judges on American Idol. Alvin invites and hires many people and celebrities to Simon's dismay before Dave returns home. The next day he takes them to mini-golf to meet his new girlfriend Samantha. The Chipmunks like her, but her son Miles is a bully who physically abuses them. Later, the Chipmunks find an engagement ring in a bag Dave brought home and believe he'll propose to Samantha, so they try to steal the ring.